A few things to note. 1 billion isn't a thousand times a million. If you make a conservative 5% let's say out of your net worth, you still need to work with a million, whereas you don't with a billion. So, technically, $400 with a million is some amount of work hours, whereas $400k with a billion is just pocket change taken out of more than most people lifetime's of earnings that is just 1 year of your interest.

Also, a lot more people (more than 1000x) have $400 to give than $400k so in a sense if people with $400 to give were all being very generous, they could amount to a lot more than what billionnaires could give.